Abstract
Membrane distillation (MD) has been increasingly explored for treatment of various hyper saline waters, including lithium chloride (LiCl) solutions used in liquid desiccant air-conditioning (LDAC) systems. In this study, the regeneration of liquid desiccant LiCl solution by a pilot direct contact membrane distillation (DCMD) process is assessed using computer simulation. Unlike previous experimental investigations, the simulation allows to incorporate both temperature and concentration polarisation effects in the analysis of heat and mass transfer through the membrane, thus enabling the systematic assessment of the pilot DCMD regeneration of the LiCl solution. The simulation results demonstrate distinctive profiles of water flux, thermal efficiency, and LiCl concentration along the membrane under cocurrent and counter-current flow modes, and the pilot DCMD process under counter-current flow is superior to that under cocurrent flow regarding the process thermal efficiency and LiCl concentration enrichment. Moreover, for the pilot DCMD regeneration of LiCl solution under the counter-current flow, the feed inlet temperature, LiCl concentration, and especially the membrane leaf length exert profound impacts on the process performance: the process water flux halves from 12 to 6 L/(m2·h) whilst thermal efficiency decreases by 20% from 0.46 to 0.37 when the membrane leaf length increases from 0.5 to 1.5 m.
Highlights
Membrane distillation (MD), a hybrid thermal-driven separation process, has been increasingly explored for treatment of various hyper saline waters due to its distinguishing attributes (Nguyen et al 2018; Abdelkader et al 2019; Duong et al 2019)
Unlike pressure-driven membrane processes, MD is less subject to the salt concentration of the feed water, and it is workable with various hyper saline waters including concentrated brine from reverse osmosis (RO) desalination (Yan et al 2017; Bindels et al 2020), diluted draw solution from forward osmosis (FO) (Nguyen et al 2018), and liquid desiccant solutions used in air-conditioning industry (Duong et al 2019; Zhou et al 2020; Liu et al 2021)
After the membrane length of 0.9 m, Tm.f remains markedly higher than Tm.d; the water vapour pressure at the feed membrane surface is lower than that at the distillate membrane surface due to the hyper salinity of the LiCl solution
Summary
Membrane distillation (MD), a hybrid thermal-driven separation process, has been increasingly explored for treatment of various hyper saline waters due to its distinguishing attributes (Nguyen et al 2018; Abdelkader et al 2019; Duong et al 2019). Unlike pressure-driven membrane processes, MD is less subject to the salt concentration of the feed water, and it is workable with various hyper saline waters including concentrated brine from reverse osmosis (RO) desalination (Yan et al 2017; Bindels et al 2020), diluted draw solution from forward osmosis (FO) (Nguyen et al 2018), and liquid desiccant solutions used in air-conditioning industry (Duong et al 2019; Zhou et al 2020; Liu et al 2021). As a thermal-driven separation technology, the MD process can be powered by low-grade waste heat or renewable solar thermal energy to reduce the process energy cost Given these notable attributes, MD has emerged as an ideal candidate to be integrated into other process for treatment of hyper saline waters with improved energy efficiency. One notable example can be the integration of MD into the liquid desiccant air-conditioning (LDAC) process (Duong et al 2017; Duong et al 2018; Lefers et al.2018; Zhou et al 2020; Zhou et al 2020)
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